34-2 House Breaker Panel Wiring

[Phr3d]

I'm in the middle of upgrading panel wiring and battery cables and I thought others may be interested in this information.

Behind the NewMar AC/DC house power panel is a series of these negative buss bars connected with 10 AWG jumpers. The positive side is a similar number of connections and jumpers. The wire is not tinned, neither are the connections sealed. That long wire actually doesn't go behind the panel, but is the return from the panel to the negative buss (which is that 12 position buss). The discolored position was where the 4 AWG cable from the engine block was connected.

We were having the Autohelm reset when we had on instruments, pressure water, refrigerator and some other stuff, probably due to low voltage.

10 AWG appears to be rated at 30 amps for 3% voltage drop in the chart below from Boat US.

Choose The Correct Wire Size

It's important to use the right sized electric cabling for any project aboard. Using the wrong one could create a plethora of problems.

www.boatus.com

 

[N.A.]

TL; DR:

- Try removing eyes from blocks, cleaning the eye contacts with a scouring pad or fine grit sandpaper, and resintalling. Might fix the problem right there.

- Check that high-current items (refrigerator, etc.) are wired to bus bar that is directly connected to battery negative terminal (and, on the other end, to breaker that has a short run to the battery positive). Stuff on the satellite bus-bar block whould be low-current stuff (in fact, even on the primary bus-bar-block, the highest current stuff should be on the bar that is connected to the battery directly, not the one jumped (even with the short jumper) to the other bar.)

That might work, and I think you'd want to connect in that manner even if you install larger dia. / smaller gauge jumpers.

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Original, longer comments:

Reading that table, it looks like that (less than 3 foot long?) jumper wire between the bus blocks (I think only one s in bus?) can handle much more current for a 3% drop; the longest jumper looks like less than 3 feet, or 1/3 of 10 ft, so you should get 3 times the current specified for 10 ft, or about 90A max. I checked this with the known resistance/length of the wire and it matches (see below; actually 100A.)

Still, you will not want to use all your allowed voltage drop at that jumper alone; you presumably have other long runs of cable where the bulk of the drop is probably occurring. So a bigger wire (smaller gauge jumpers) might be worth it...

--> But it might work fine to just make sure / double check that all high-current stuff is wired to the bus bar/block connected directly to the battery via large diamater wire, and only lower-current-draw stuff on the satellite bus bar/block connected to the first by that long jumper. Then there will never be much current on (or voltage drop across) the long jumper. I.e., keep the runs to the high current items short, and the low current items can have longer runs (involving jumpers.) I suspect that is normal best practice.

The small jumpers (not even 6 inches, I assume) should be able to handle 600A (since they are 1/6 the length of the 3' one) before hitting 3% = 0.36V drop. Again, you don't want all your 3% loss at that one jumper, but I also suspect you are not running 600A... even at 100A, which sounds high, you'd be at 0.5% loss through a short jumper wire. So highest-current stuff on the primary bus bar wired straight to the battery negative terminal might well be fine unless you have a really long cable run from that block to wherever the item is (maybe the stern? or a bow windlass?)

Realistically, I suspect that if you are running into voltage drop problems the more likely culprit is the connections you mentioned -- unsealed, corroded, etc. Cleaning (or replacing) those might make all the difference. It's not that hard to get a few 1/10's of an Ohm in contact resistance from corroded contacts, and even at 10A, 1 Ohm would give 1V drop (= over 8% of 12V.) With maybe 4 connectors in series there on the jumpers, if corroded then an Ohm total seems very possible.

FYI: My world also involves tinning (and soldering more generally But I discovered boats do not use soldered connections much (nor aircraft, nor cars); apparently the vibration can cause the solder joints to fail/wires to fatigue. Instead, those crimp-connections I always thought were cheesy turn out to be... not cheesy. A good crimp (which requires a proper crimp tool, which is not cheap; do not do it with pliers) cold-welds the wires (and maybe connector) together, which is apparently much more reliable. My guess is the eye connectors on your jumpers were (if original to the boat) probably properly crimped on; if so, then the contact resistance just comes mainly from corrosion of the eye itself where it is contacting the bus bar. Others here will know better whether it is preferable to just replace the eyes (requiring new jumpers and maybe buying the right crimp tool), but certainly taking the jumpers off and cleaning the eyes properly (I'm lazy and would use fine-grit sandpaper or one of those green pot scrubbers, but one can get actual contact cleaner) would let you test whether it was contact resistance causing the problem -- just remove, clean (by buffing the eyes with the scouring pad or fine git sandpaper), and re-install. If the problem goes away, that was it. New eyes might make for a longer interval before you have to repeat the process; I am not sure. But in any case, soldering/tinning is not necessarily recommended.
However, MaineSail is/was a real expert, an he (and apparently NASA) says it's OK to crimp the connector on, then solder the crimped connection, as long as you do it right:

A Question For Mainesail - Soldering?

Maine, I read your crimper tests, and am as always impressed with the way you go about your tests. Not only expertly but in a logical progression. With regard to the crimper test, I am curious as to whether or not you considered a testing a crimp/solder connection. I always use the cheapo...

forums.sailboatowners.com

Marine Wire Termination - Marine How To

Marine Wire Termination - Tools of the Trade MHT Recommended Tools: The products below are our top picks for crimp tools. RecommendationsI include; PRO GRADE, MARINE GRADE, & PENNY SAVER GRADE. Every tool recommended BELOW, we have tested here.

marinehowto.com

Note: Maine Sail / Marine How To / Compass Marine had a bad stroke a couple of years ago; I think the site is now legacy. Consider donating if you use it -- I am pretty sure all help is deeply appreciated.

PS: Calculation double-check: the resistance/foot for 10-gauge copper wire is < 1.2 milliOhms/foot (at 149 deg F, i.e. if the wire got hot)

Copper Wire - Electrical Resistance vs. Gauge

Gauge, weight, circular mils and electrical resistance in copper wire.

www.engineeringtoolbox.com

So it will give a 3% of 12V = 0.36V drop for a 3 ft run at
I = 0.36V/(3 ft * 1.2 mOhms/ft) = 100A, which matches what I suggested above.

Disclaimer: I am not expert on boat wiring (but I do have a fair bit of technical training.)

 

[bigd14]

When I rewired my boat I found that all the original non-tinned copper wires were dark and slightly corroded even in the middle of a long run. I never found any “fresh” copper while cutting it all out. I bet that aging adds a lot of cumulative voltage drop and resistance to the system.

 

[Phr3d]

"dark and slightly corroded"

I had some help changing throttle cables (wow, new ones are cool!) which resulted in the cover of the UV degraded shore power socket cover being broken. I had so many other stickies that were not getting done, I was a little frazzled with adding another one but, I had some rewards points stockpiled and was able to get a bitchin stainless upgrade.

The point though, when I was in there, the green and black wires looked fine...





The better news is that with all the new demands on the house battery system, the autopilot didn't hiccup once on the last trip. This was with the 4.8A USB ports charging iPads, iPhones, earbuds, running 2 chart plotters, pressure water on, cabin lights on, etc. I did replace the jumpers on the boards with 4 AWG and replaced the buss bars with ones requiring less connections. I'm pretty confident that the windless (and maybe water maker) will be happy on the new wiring as well. The inverter charged the dinghy battery without any drama. This means the microwave (going back in this week) is a very real way to not have cold leftovers while on anchor.


Is there any advice on an AC shore/inverter switch kind of thing?


Solar going on this coming week.